The present invention relates to methods of drying and activating catalysts, particularly zeolite based catalysts.
Catalysts are widely employed in the petrochemical industry, particularly in reforming operations for converting normal paraffins and other less desired constituents of a hydrocarbon feedstock to desirable aromatic compounds. The catalysts employed for these purposes typically include a base and one or more metals, most typically platinum, dispersed on the base, and may also include a binder for physically supporting the base.
Reforming catalysts typically are prepared by depositing salts of the metal on the base and then calcining the base with the deposited salts in an oxidizing atmosphere to convert the metals to oxides and/or metallic oxide complexes including the metals, oxygen and other components, typically chlorine. The catalyst in this oxidized condition ordinarily is loaded into a reactor and contacted with hydrogen at an elevated temperature to reduce the metallic oxides or oxide complexes to free metal and thus bring the catalyst to its reduced or active state. In a typical reforming process, the hydrocarbon feedstock is passed through the reactor together with hydrogen at an elevated temperature. Under these conditions, some of the paraffins in the feedstock react to form the desired aromatic products upon contact with the reduced or activated catalyst. After the catalyst has been so employed for a prolonged period, it typically loses some potency and accordingly is regenerated by processes which may include exposing the catalyst to oxygen so as to burn off carbonaceous deposits accumulated on the catalyst during the process. The regenerated catalyst, once again in the oxidized state with the metals in the form of oxides or oxide complexes, is again reduced and the process is repeated.
The nature of the base and the distribution of the metal on and in the base can significantly affect the performance of the catalyst. Catalysts incorporating a zeolite base, notably a type L zeolite base may be employed in reforming operations as set forth in U.S. Pat. No. 4,104,320, the disclosure of which is incorporated by reference herein. A "type L zeolite" is a zeolite having a particular crystal structure as further set forth hereinbelow. Type L zeolite-based catalysts typically provide good selectivity and hence promote conversion of the feedstock to the desired aromatic products rather than less desired by-products. As set forth in copending, commonly assigned U.S. patent application Ser. No. 550,952, filed Nov. 10, 1983 (U.S. Pat. No. 4,595,668), the disclosure of which is also incorporated by reference herein, the activity and selectivity of a type L zeolite based catalyst are markedly improved by dispersing the metallic oxide or metallic oxide complex within the pores or channels of the zeolite so that, prior to reduction, the metallic oxide or oxide complex is disposed principally within the pores in the form of particles having a diameter of less than about 7 angstroms. Zeolite based catalysts have become increasingly important in reforming operations with the advent of the particular improved type L zeolites with a cylindrical morphology described in U.S. Pat. No. 4,544,539, the disclosure of which is also incorporated by reference herein. These zeolites provide, inter alia increased catalyst life in conjunction with the other benefits of type L zeolite catalyst bases.
Zeolite based catalysts, including the aforementioned type L zeolite based catalysts, typically are hygroscopic. Thus, although freshly calcined new catalyst is dry, the catalyst absorbs moisture when it is exposed to the ambient atmosphere, as during loading of the catalyst into the reactor. These catalysts will likewise absorb moisture if the reactor is opened to the atmosphere, as for service or repair of internal components. In many reforming operations the catalyst must be dry when contacted with the feedstock. Accordingly, there have been increasing needs for practical methods of drying a zeolite-based catalyst and for methods of reducing or activating such catalysts.